1. Solving a pain-point of many people re: hailing a cab, via an app that works everywhere.
2. Using VC funds to (initially) pay drivers more than you, the customer, were paying them.
3. Ignoring local regulations and passing the savings/convenience on to you.
1 is nice but I don't think they established much of a moat (both drivers and customers are willing to use multiple apps); 2 isn't sustainable in the long-term, and they failed to leverage 3 to establishing a permanent right to operate as they had been in most markets.
I think this makes Uber an even more interesting benchmark for other unicorns, since besides "solving a real problem without establishing a moat" they are also often burning through VC cash to prop up their business model while ignoring some laws which they may not be able to get away with ignoring long-term.